8-INCH SiC SINGLE CRYSTAL SUBSTRATE

ABSTRACT

An 8-inch SiC single crystal substrate of an embodiment has a diameter in a range of 195 mm to 205 mm, a thickness in a range of 300 μm to 650 μm, a SORT of 50 μm or less, and an in-plane variation of the thickness of the substrate, which is the difference between the maximum and minimum substrate thickness at the center of the substrate and four points on the circumference of a circle having a radius half the radius of the substrate, is 1.5 μm or less.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to an 8-inch SiC single crystalsubstrate.

Priority is claimed on Japanese Patent Application No. 2022-090464,filed on Jun. 2, 2022, the content of which is incorporated herein byreference.

Description of Related Art

Silicon carbide (SiC) has a breakdown electric field larger by one digitthan and the band gap three times larger than those of silicon (Si).Moreover, silicon carbide (SiC) has characteristics such as thermalconductivity being about three times higher than silicon (Si). Siliconcarbide (SiC) is expected to be applied to power devices, high frequencydevices, high temperature operation devices, and the like. For such SiCdevices, a SiC epitaxial wafer is used recently.

SiC epitaxial wafers are obtained by laminating a SiC epitaxial layer onthe surface of a SiC single crystal substrate. Hereafter, the substratebefore the lamination of the SiC epitaxial layer is referred to as a SiCsingle crystal substrate, and the substrate after the lamination of theSiC epitaxial layer is referred to as a SiC epitaxial wafer. SiC singlecrystal substrates are cut from a SiC single crystal ingot.

The mainstream of the current market for SiC single crystal substratesis SiC single crystal substrates with a diameter of 6 inches (150 mm),but the development for mass production of SiC single crystal substrateswith a diameter of 8 inches (200 mm) is progressing, and full-scale massproduction is beginning. Increasing production efficiency and reducingcosts by increasing the diameter from 6 inch to 8 inch is expected tofurther popularize SiC power devices as the most effective means inenergy-saving technologies.

In manufacturing the next generation of large-diameter SiC singlecrystal substrates, the same quality cannot be obtained by applying themanufacturing conditions optimized for the manufacture of SiC singlecrystal substrates with current size. This is because new problems arisewith each new size. For example, Patent Literature 1 describes a problemthat when a manufacturing technique of a 4-inch SiC single crystalsubstrate is applied to the manufacture of a 6-inch SiC single crystalsubstrate, thermal decomposition frequently occurs around the outerperipheral portion of the seed crystal, which causes macro defects, andtherefore, single crystals with high crystal quality are not obtainedwith good yield. Patent Literature 1 describes an invention that solvesthe problem by using seed crystals of a given thickness. In this way, itis necessary to establish the manufacturing conditions for SiC singlecrystal substrates with new sizes while solving new problems that havearisen in response to new sizes.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Examined Patent, No. 6594146-   Patent Literature 2: Japanese Examined Patent, No. 6598150-   Patent Literature 3: Japanese Unexamined Patent Application, First    Publication No. 2020-17627-   Patent Literature 4: Japanese Unexamined Patent Application, First    Publication No. 2019-189499

The SiC single crystal substrate is obtained through the SiC singlecrystal ingot fabrication process and the SiC single crystal substratefabrication process to fabricate the SiC single crystal substrate fromthe SiC single crystal ingot. To establish manufacturing technology for8-inch SiC single crystal substrates, it is necessary to solve newproblems specific to 8-inch substrates in each of the SiC single crystalingot fabrication process and the SiC single crystal substratefabrication process.

New problems specific to 8-inch substrates include, for example,obtaining an 8-inch substrate with the same dislocation density as thatof a 6-inch substrate in the SiC single-crystal ingot fabricationprocess. When an 8-inch substrate is manufactured simply by applying aSiC single crystal substrate fabrication technique optimized for themanufacture of 6-inch substrates, an 8-inch substrate with a dislocationdensity higher than that of a 6-inch substrate is produced. The largerthe size, the greater the hurdle to get the same quality. Therefore,when evaluating the technical significance of the manufacturingtechnique of 8-inch SiC single crystal substrates, the dislocationdensity of 8-inch substrates obtained by simply applying themanufacturing technique of SiC single crystal substrates optimized forthe manufacture of 6-inch substrates is the starting point, and thetechnical significance should be evaluated by how much the dislocationdensity of the starting point has been improved on the basis of thedislocation density of the starting point.

On the other hand, the yield of 8-inch SiC single crystal substrates inmass production is determined by the same or more stringent evaluationcriteria as 6-inch SiC single crystal substrates. Each step ofimprovement leads to the establishment of manufacturing technology for8-inch SiC single crystal substrates.

In view of the above circumstances, the present disclosure has been madeto provide an 8-inch SiC single crystal substrate having characteristicsthat have not been realized in an 8-inch SiC single crystal substrate.

SUMMARY OF THE INVENTION

The present disclosure provides the following means to solve the aboveproblems.

An aspect of the present disclosure provide an 8-inch SiC single crystalsubstrate, wherein the diameter is in a range of 195 mm to 205 mm, thethickness is in a range of 300 μm to 650 μm, SORI is 50 μm or less, andthe in-plane variation of the thickness of the substrate, which is thedifference between the maximum and minimum substrate thickness at thecenter of the substrate and four points on the circumference of a circlehaving a radius half the radius of the substrate, is 1.5 μm or less.

In the SiC single crystal substrate according to the above aspect, theSORI may be 40 μm or less.

In the SiC single crystal substrate according to the above aspect, theSORI may be 30 μm or less.

In the SiC single crystal substrate according to the above aspect, theSORI may be 20 μm or less.

In the SiC single crystal substrate according to the above aspect, thein-plane variation of the thickness of the substrate may be 1.0 μm orless.

In the SiC single crystal substrate according to the above aspect, thedensity of micropipe defects may be 1/cm² or less, and the total numberof etch pits appearing by KOH etching performed at 550° C. for 10minutes may be 5×10⁹ or less.

In the SiC single crystal substrate according to the above aspect, thetotal number of etch pits may be 5×10⁸ or less.

In the SiC single crystal substrate according to the above aspect, thetotal number of etch pits may be 5×10⁷ or less.

In the SiC single crystal substrate according to the above aspect, thedensity of etch pits identified as threading dislocations may be2×10³/cm² or less, and the density of etch pits identified as basalplane dislocations may be 5×10³/cm² or less.

The 8-inch SiC single crystal substrate of the present disclosure canprovide an 8-inch SiC single crystal substrate having characteristicsthat have not been realized in an 8-inch SiC single crystal substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a SiC single crystal substrateaccording to the present embodiment.

FIG. 2 is a conceptual diagram showing the definition of SORI.

FIG. 3 is a conceptual diagram showing the process of reducing thework-affected layer depth by mechanical machining.

FIG. 4 is a schematic cross-sectional view of a SiC single crystalmanufacturing apparatus.

FIG. 5 is a schematic cross-sectional view of another example SiC singlecrystal manufacturing apparatus.

FIG. 6A is a schematic cross-sectional view of the driving means formoving the heat-insulating member up and down in the SiC single crystalmanufacturing apparatus.

FIG. 6B is a schematic cross-sectional view of the driving means formoving the heat-insulating member up and down in the SiC single crystalmanufacturing apparatus.

FIG. 6C is a schematic cross-sectional view of the driving means formoving the heat-insulating member up and down in the SiC single crystalmanufacturing apparatus.

FIG. 7A is the positional relationship between the bottom surface of theheat-insulating member and the surface of the single crystal, and therelationship between the positional relationship and the isothermalsurface in the vicinity of the single crystal.

FIG. 7B is the positional relationship between the bottom surface of theheat-insulating member and the surface of the single crystal, and therelationship between the positional relationship and the isothermalsurface in the vicinity of the single crystal.

FIG. 7C is the positional relationship between the bottom surface of theheat-insulating member and the surface of the single crystal, and therelationship between the positional relationship and the isothermalsurface in the vicinity of the single crystal.

FIG. 8A is a schematic diagram illustrating the shape of the isothermalsurface near a single crystal during crystal growth.

FIG. 8B is a schematic diagram illustrating the shape of the isothermalsurface near a single crystal during crystal growth.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present embodiment will be described in detail withreference to the drawings. The drawings used in the followingdescription may show, for convenience's sake, the features of thepresent disclosure in enlarged form, and the dimensional proportions ofthe components may be different from those in practice. The materials,dimensions, and the like exemplified in the following description areonly examples, and the present disclosure is not limited thereto, andthe disclosure can be carried out by appropriately changing the gistthereof without changing it. In addition, in each figure, componentsknown to those skilled in the art other than those described in thefigure may be omitted.

(SiC Single Crystal Substrate)

FIG. 1 is a schematic plan view of a SiC single crystal substrateaccording to the present embodiment.

The SiC single crystal substrate 1 shown in FIG. 1 is an 8-inch SiCsingle crystal substrate with a diameter in a range of 195 mm to 205 mm,a thickness in a range of 300 μm to 650 μm, SORI is 50 μm or less, andthe in-plane variation of the thickness of the substrate is 2.0 μm orless.

Although there are no particular restrictions on the outer shape of theSiC single crystal substrate 1, substrates with various flat shapes andvarious thicknesses can be used, but the substrate is typicallydisk-shaped. The thickness of the SiC single crystal substrate can be inthe range of, for example, 300 μm to 650 μm.

SiC single crystal substrate 1 is preferably 4H-SiC, because SiC comesin a variety of polytypes, but 4H-SiC is mainly used to make practicalSiC devices.

One side of the SiC single crystal substrate 1 is the surface (the mainsurface) on which the SiC epitaxial layer is formed. It is preferablethat the main surface is the c-plane (the (0001) plane of the 4H-SiCcrystal) or a surface inclined at an inclination angle (off angle)greater than 0° and less than 10° with respect to c-plane. It is a4H-SiC type single crystal wafer. The off-angle is preferably greaterthan 0° and less than 10° in the <11-20> direction of the c-plane.

Since the larger the off angle, the smaller the number of wafersobtained from the SiC single-crystal ingot, the smaller the off angle ispreferable from the viewpoint of cost reduction. SiC single crystalsubstrates with an off-angle of, for example, 0.4° to 5° can be used.0.4° can be said to be the lower limit as the off angle at whichstep-flow growth is possible.

The SiC single crystal substrate may contain impurities depending on theapplication. For example, nitrogen (n-type), boron, aluminum (p-type),etc. can be included to adjust its conductivity or resistivity.

The main surface (hereinafter, this surface may be referred to as the‘front surface’.) of the SiC single crystal substrate 1 is a mirrorsurface. This is because that it is necessary to form an epitaxial layeron the front surface of the SiC single crystal substrate by theepitaxial growth of SiC single crystal in order to fabricate various SiCdevices. The mirror surface of the front surface is formed bymirror-finishing the surface of the cut substrate, which is obtained bycutting a part to be substrate from a SiC single crystal ingotmanufactured using sublimation method or the like.

The other surface (hereafter, this surface may be referred to as the‘back surface’.) need not be a mirror surface, but in the case of a SiCsingle crystal substrate whose front surface is a mirror surface andwhose back surface is not, a difference in residual stress occursbetween the front surface and the back surface, and the substrate iswarped to compensate for the residual stress (Twyman effect). By makingthe back surface also mirror surface, the warp of the substrate causedby the Twyman effect can be suppressed. A method has been developed tofabricate a SiC single crystal substrate with low warp, whose frontsurface is mirror-finished and whose back surface is not mirror-finished(see, e.g., Patent Literature 2).

The SiC single crystal substrate 1 has a notch 2, which is a marker ofthe crystal orientation, but may have OF (orientation flat) instead ofnotch 2.

The SORI of the SiC single crystal substrate 1 is preferably 50 μm orless, more preferably 40 μm or less, more preferably 30 μm or less, andmore preferably 20 μm or less.

SORI is one of the parameters that indicates the degree of warp of thesubstrate, and is expressed as the sum of the normal distances from theleast square plane calculated by the least-squares method using all thedata on the surface of the substrate to the highest and lowest points onthe surface of the substrate when measured to support the back surfaceof the substrate without changing the original shape of the substrate.That is, when the least square plane of the substrate surface is takenas the reference height (least square plane height), as shown in FIG. 2, the figure shows the sum ((a)+(b)) of the distance (a) between theheight at the highest point of the substrate surface and the referenceheight, and the distance (b) between the height at the lowest point andthe reference height.

The thickness of the work-affected (work-altered) layers on both thefront and back sides of the SiC single crystal substrate 1 is preferably0.1 nm or less.

<Relationship Between Work-Affected Layer and SORI>

The SiC single crystal substrate is prepared by slicing SiCsingle-crystal ingot and flattening the surfaces. Such mechanicalprocessing introduces distortion due to the mechanical processing intothe surface of the substrate. The layer where the processing distortionoccurs on the surface of a SiC single crystal substrate is called awork-affected (work-altered) layer as described above. When awork-affected layer (work-altered layer) is formed on the front and backsurfaces, the difference in the processing distortion occurs on thefront and back surfaces, and the difference also occurs in the residualstress, causing the warp of the substrate by the Twyman effect. Theshape or the warp of the substrate is determined by the balance ofstress conditions generated by the work-affected layers on both sides ofthe substrate.

FIG. 3 is a conceptual diagram showing the process of reducing the depthd (d1, d2, d3, d4) of the work-affected layer by mechanical processing.For example, FIG. 3(a) is a conceptual cross-sectional view near thesurface after lapping process, FIG. 3(b) is a conceptual cross-sectionalview near the surface after polishing process, FIG. 3(c) is a conceptualcross-sectional view near the surface after finish-grinding, and FIG.3(d) is a conceptual cross-sectional view near the surface after CMP.

FIG. 14 of Patent Literature 3 shows the relationship between the depthof the work-affected layer of a single-crystal SiC wafer and SORI. Thegraph shows that the deeper the work-affected layer, the larger the SORIvalue. Also, when comparing a 6-inch SiC single crystal substrate with a4-inch SiC single crystal substrate, the 6-inch SiC single crystalsubstrate was more susceptible to the work-affected layer than the4-inch SiC single crystal substrate, resulting in a larger SORI.Therefore, when comparing an 8-inch SiC single crystal substrate with a6-inch SiC single crystal substrate, it is inferred that the 8-inch SiCsingle crystal substrate is more susceptible to the effect of thework-affected layer, resulting in a larger SORT. Therefore, it is moreimportant to remove the work-affected layer to reduce the warp for the8-inch SiC single crystal substrate than for the 6-inch SiC singlecrystal substrate.

The in-plane variation of the substrate thickness of the SiC singlecrystal substrate 1 is 2.0 μm or less. The in-plane variation of thethickness is preferably 1.5 μm or less, and more preferably 1.0 μm orless.

In the SiC single crystal substrate according to the present embodiment,reduction of in-plane variation in thickness is realized by performinglapping using a novel lapping slurry.

In the present specification, “in-plane variation in substratethickness” is expressed as the difference between the maximum andminimum values obtained of the thicknesses of a SiC single crystalsubstrate measured by a dial gauge or the like at five points (onecenter point and four points (positions shown as reference signs 1 a to1 e in FIG. 1 ) on the circumference of a circle having a radius halfthe radius of the substrate).

FIG. 14 in Patent Literature 3 shows the relationship between the depthof the work-affected layer, which is one parameter for the work-affectedlayer, and SORI. In developing an 8-inch SiC single crystal substratewith high yield, the inventor focused on in-plane variations in thedepth of the remaining work-affected layer.

Even though the work-affected layer can be almost completely removedwhen the planarization process is carried out over a sufficiently longtime at the laboratory level, it is assumed that the work-affected layerwill remain somewhat when the planarization process is carried out in apractical time. In addition, although the depth d of the work-affectedlayer conceptually shown in FIG. 3 is drawn assuming an average depth,it is not exactly a uniform depth in reality, and it is assumed that athin work-affected layer remains over the entire surface to have aslight variation in depth, or a work-affected layer remains locally onthe surface. In such a case, it is inferred that the effect of thein-plane variation in the depth of the work-affected layer on SORI isgreater in the case of an 8-inch SiC single crystal substrate than inthe case of a 6-inch SiC single crystal substrate.

The in-plane variation in the substrate thickness of the SiC singlecrystal substrate 1 is considered to reflect the in-plane variation inthe depth of the work-affected layer.

The density of micropipe defects in the SiC single crystal substrate 1is preferably 1/cm² or less.

In the SiC single crystal substrate 1, the total number of etch pitsappearing by KOH etching is preferably 5×10⁹ or less, more preferably5×10⁸ or less, and even more preferably 5×10⁷ or less. In this case, KOHetching was performed at 550° C. for 10 minutes.

The total number of etch pits corresponds to the total number ofdislocations.

In the SiC single crystal substrate 1, the density of the etch pitsidentified as threading dislocations (TD) is preferably 2×10³/cm² orless and the density of the etch pits identified as basal planedislocations is preferably 5×10³/cm² or less.

The density of etch pits identified as threading dislocations (TD) ismore preferably 1×10³/cm² or less, and even more preferably 5×10²/cm² orless.

The density of etch pits identified as the basal plane dislocations ismore preferably 2×10³ pits/cm² or less, more preferably 1×10³ pits/cm²or less, and more preferably 5×10² pits/cm² or less.

Here, threading dislocation is a combination of threading screwdislocation (TSD) and threading edge dislocation (TED).

The type of dislocation can be determined from the shape of the etchpits that appear by KOH etching using an optical microscope or the like,and the number of etch pits per unit area can be counted. In general, anetch pit with a medium hexagonal shape corresponds to a threading screwdislocation (TSD), an etch pit with a small hexagonal shape correspondsto a threading edge dislocation (TED), and an etch pit with anelliptical shape (shell shape) corresponds to a basal plane dislocation(BPD). In addition, an etch pit with a large hexagonal shape correspondsto a micropipe (MP).

(Method of Manufacturing SiC Single Crystal Substrate)

The method of manufacturing a SiC single crystal substrate according tothe present embodiment is explained separately for the fabricationprocess of a SiC single crystal ingot and the fabrication process of theSiC single crystal substrate from the ingot.

<Fabrication Process of SiC Single Crystal Ingot>

Continuing intense research, the inventor found that more precisecontrol of temperature gradients in the radial and vertical directions(crystal growth direction) for a SiC single crystal ingot with 6-inchdiameter was a key point in the fabrication of a SiC single crystalingot with 8-inch diameter. It was found that more precise control ofthe temperature gradient in the radial and vertical directions (crystalgrowth direction) could be realized by applying the method disclosed inPatent Literature 4. Specifically, a SiC single crystal manufacturingapparatus with a heat-insulating member that can move along theextending direction of the guide member outside the guide member thatguides crystal growth can be used. It is not limited to the methoddisclosed in Patent Literature 4 as a method for more precise control oftemperature gradients in the radial and vertical directions (crystalgrowth direction).

In the transition to the large diameter SiC single crystal ingot, theapplication of the fabrication method of SiC single crystal ingots withconventional diameter does not yield large diameter SiC single crystalingots with similar crystal quality. For example, the following problemsoccurred during the transition from a 4-inch diameter SiC single crystalingot to a 6-inch diameter SiC single-crystal ingot (see PatentLiterature 1).

In the growth of SiC single crystals by the sublimationrecrystallization method using a seed crystal, it is necessary to makethe surface shape of the ingot during growth to be nearly convex in thegrowth direction as one of the growth conditions to realize high crystalquality. This is because, for example, in the case of 4H-type SiC singlecrystals used in power devices, when growing roughly parallel to the<0001> axis, i.e., the c-axis direction of the crystal, the SiC singlecrystal grows by the evolution of spiral steps extruded from thethreading screw dislocations. Therefore, it is said that by beinggenerally convex, there is essentially a single step supply source onthe growth surface to being able to improve the polytype stability. Ifthe growth surface has a concave surface or multiple convex parts, therewill be multiple sources supplying growth steps and steps delivered fromdifferent sources will collide. In such a case, not only defects such asdislocations are generated from the parts where they collide, but alsothe state of atomic stacking in the c-axis direction, which is unique tothe 4H-type polytypes, becomes easily disturbed, so that different kindsof polytypes with different stacking structures, such as the 6H-type andthe 15R-type, are generated and micropipe defects are generated.

Therefore, for example, in order to stabilize a 4H-type polytypesuitable for power devices and grow a so-called single polytype crystalcomposed of only 4H-type polytype, it is important to make the growthsurface shape of the grown crystal roughly convex. Specifically, theconvex shape of the grown crystal is realized by optimizing thetemperature at the center of the grown crystal in terms of the growthrate, etc., and by controlling the temperature distribution duringgrowth, that is, the shape of the isotherm, so that it becomes roughlyconvex. It was thought that the SiC single-crystal ingot grown undersuch growth conditions where the roughly convex isotherm was realizedwould grow to be approximately parallel to the isotherm, therebyensuring the above polytype stability.

However, when the diameter of a growing crystal is more than 150 mm (6inches), if the temperature at the center of the growing crystal isoptimized to be equivalent to that of a conventional single crystalgrowth of 100 mm (4 inches) in terms of growth rate, etc., whilecontrolling the temperature gradient during growth so that the growthsurface shape of the growing crystal is roughly convex in the growthdirection, the temperature around the seed crystal inevitably becomeshigher than that in the case of small diameter crystal growth. As aresult, there was a problem that the SiC single crystal of the seedcrystal itself was easily pyrolyzed at the periphery on the outer side.For this problem, Patent Literature 1 solved the problem by using a seedcrystal composed of a silicon carbide single crystal with a thickness of2.0 mm or more as the main solution.

In the present disclosure, in order to fabricate a SiC single crystalingot with 8-inch diameter, we have succeeded in fabricating a SiCsingle crystal ingot with 8-inch diameter having characteristicscomparable to those of a SiC single-crystal ingot with 6-inch diameterby controlling not only the temperature gradient in the radial directionbut also the temperature gradient in the vertical direction (the crystalgrowth direction) using a heat insulating member that can move along theextending direction of the guide member on the outside of the guidemember to guide the crystal growth, as is not the typical method forfabricating a SiC single crystal ingot with 6-inch diameter as shown inPatent Literature 1. The SiC single crystal manufacturing apparatus andthe fabrication process of a SiC single crystal ingot is describedbelow.

FIG. 4 is a schematic cross-sectional view of an example of a SiC singlecrystal manufacturing apparatus for carrying out the fabrication processof SiC single crystal ingots.

The SiC single crystal manufacturing apparatus 100, as shown in FIG. 4 ,includes a crucible 10, a seed crystal installation part 11, a guidemember 20, and a heat-insulating member 30. In FIG. 4 , a raw materialG, a seed crystal S, and a single crystal C grown on the seed crystal Sare illustrated simultaneously for better understanding.

As shown in the drawings, a direction in which the seed crystalinstallation part 11 and the raw material G face each other is definedas a vertical direction, and a direction perpendicular to the verticaldirection is defined as a left-and-right direction.

The crucible 10 surrounds a film formation space K in which the singlecrystal C grows. A well-known crucible may serve as the crucible 10 aslong as it is a crucible which can produce the single crystal C by asublimation method. For example, a crucible made of graphite, tantalumcarbide or the like can be employed. The crucible 10 is hot duringgrowth, which is necessarily formed of a material tolerable to hightemperature. For example, graphite has a very high sublimationtemperature of 3550° C., and thus is tolerable to the high temperatureduring growth.

The seed crystal installation part 11 is provided at a position facingthe raw material G in the crucible 10. A raw material gas can beefficiently supplied to the seed crystal S and the single crystal Csince the seed crystal installation part 11 is located at a positionfacing the raw material G.

The guide member 20 extends from a periphery of the seed crystalinstallation part 11 toward the raw material G. That is, the guidemember 20 is disposed along a crystal growth direction of the singlecrystal C. Consequently, the guide member 20 serves as a guide when thesingle crystal C crystal-grows from the seed crystal S. Crystal growthis carried out on an inner side, that is, on an inner surface side ofthe guide member 20.

A lower end of the guide member 20 is supported by a support 21. Thesupport 21 closes a space between the lower end of the guide member 20and the crucible 10 to suppress entry of the raw material gas into aregion outside the guide member 20. If the raw material gas intrudesinto the region, polycrystals grow between the guide member 20 and theheat-insulating member 30, and the free movement of the heat-insulatingmember 30 is inhibited.

A connection between the guide member 20 and the support 21 ispreferably a caulking structure. The caulking structure is a structuredesigned to tighten the connection between the guide member 20 and thesupport 21 in case where physical force is applied to the guide member20. For example, a screw structure in which the connection is threadedis an example of the caulking structure. The guide member 20 may be inphysically contact with the crystal-grown single crystal C, in which theguide member 20 can be prevented from falling off.

The guide member 20 in FIG. 4 extends vertically in the verticaldirection. The shape of the guide member 20 is not limited to the shapeshown in FIG. 4 , and examples of the shape includes a tubular shapesuch as a cylindrical shape, and a truncated cone. A thickness of theguide member may be uniform. A length, an inner diameter and an outerdiameter of the member may be optionally selected. FIG. 5 is a schematiccross-sectional view showing another example of the SiC single crystalmanufacturing apparatus 101 according to the embodiment. The guidemember 25 in FIG. 5 is expanded in diameter toward the raw material Gfrom the seed crystal installation part 11. The diameter of the singlecrystal C can be increased by expanding the diameter of the guide member25.

An upper end of the guide member 20 is open in the example shown in FIG.4 . However, the upper end of the guide member 20 may be connected to aninner surface of the crucible 10 to close a space where theheat-insulating member 30 is provided.

A surface of the guide member 20 is preferably coated with tantalumcarbide. The guide member 20 is always exposed to the raw material gasto control the flow of the raw material gas. For example, in a casewhere the guide member 20 is formed of graphite and the guide member 20is used while graphite is completely exposed, graphite may react withthe raw material gas to be deteriorated and get damaged. Deteriorationand damage of graphite may cause the guide member 20 to be perforated,and also cause a phenomenon that carbon powder peeled by degradation istaken into the single crystal C and the quality of single crystal Cbecomes worse. Meanwhile, tantalum carbide can tolerable to hightemperature and does not cause an undesirable reaction with the rawmaterial gas. Therefore, high-quality SiC single crystal growth can bestably performed. The guide member 20 may be formed of tantalum carbideonly.

The heat-insulating member 30 is movable along an extension direction ofthe guide member 20 on the outside of the guide member 20. The outsideof the guide member 20 may indicate an outer surface side of the guidemember. A position of a surface Ca of the single crystal C can move dueto growth. The heat-insulating member 30 is moved, whereby it ispossible to control a positional relationship between an end surface ona raw material G side of the heat-insulating member 30 (hereinafterreferred to as a lower surface 30 a) and the surface Ca of the singlecrystal C. Therefore, a temperature distribution in the vicinity of thesurface Ca of the single crystal C can be freely controlled, and asurface shape of the crystal-grown single crystal C can also be freelycontrolled. In the process of crystal growth, the positionalrelationship between the end surface 30 a on the raw material side ofthe heat-insulating material 30 and the surface Ca of the single crystalC can be controlled. In addition, the end surface 30 a on the rawmaterial side of the heat insulating material 30 can be located within20 mm from the surface Ca of the single crystal C during the crystalgrowth process. Further, in the process of crystal growth, the endsurface 30 a on the raw material side of the heat-insulating material 30can be located closer to the seed crystal installing portion 11 withrespect to the surface Ca of the single crystal C. The thickness of theheat-insulating material 30 can be set to half or less of the growthamount of the SiC single crystal ingot manufactured to be 0.2 mm ormore.

FIGS. 6A to 6C are schematic cross-sectional views, each showing apreferred example of a driver for moving the heat-insulating member 30up and down. The driver is not particularly limited as long as theheat-insulating member 30 can be moved in the vertical direction. Forexample, as shown in FIG. 6A, a driving member 31 extending to theoutside of the crucible 10 from an upper portion of the heat-insulatingmember 30 may be provided to move the heat-insulating member 30 bypushing and pulling the driving member up and down. An upper surface ofthe crucible 10 may be provided with a notch or an opening for passingthe driving member. For example, as shown in FIG. 6B, a lift-typedriving member 32 may be provided such that the heat-insulating member30 may be supported from a lower portion thereof. For example, as shownin FIG. 6C, a notch or opening may be provided in part of a side surfaceof the crucible 10, and a driving member 33 extending to the outside ofthe crucible 10 may be provided through the notch or opening to move theheat-insulating member 30 by raising and lowering the driving member.

The heat-insulating member 30 is preferably made of a material havingthermal conductivity of 40 W/mk or less at high temperature of 2000° C.or more. Examples of the material having thermal conductivity of 40 W/mkor less at high temperature of 2000° C. or more include a graphitemember having thermal conductivity of 120 W/mk or less at normaltemperature. Moreover, it is more preferable that the heat-insulatingmember 30 is formed of a material having thermal conductivity of 5 W/mkor less at high temperature 2000° C. or more. Examples of the materialhaving thermal conductivity of 5 W/mk or less at high temperature 2000°C. or more include a felt material mainly containing graphite andcarbon.

The shape of the heat-insulating member 30 is appropriately designed inaccordance with a shape of a region sandwiched by the guide member 20and the inner surface of the crucible 10. The shape of theheat-insulating member can be optionally selected, and may be, forexample, donut shaped. As shown in FIG. 4 , in a case where a distancebetween the guide member 20 and the inner surface of the crucible 10 isconstant, the heat-insulating member 30 can be arranged to fill in a gapbetween them. As shown in FIG. 5 , in a case where the distance betweenthe guide member 25 and the inner surface of the crucible 10 varies, theshape of the heat-insulating member 30 can be designed in accordancewith the position at which the gap between them is the narrowest suchthat a width of the heat-insulating member 30 is adjusted to be the sameas or smaller than a distance at which the gap between them is thenarrowest. With such a design, the heat-insulating member 35 is movable,and immovable clogging between the guide member 25 and the inner surfaceof the crucible 10 can be avoided.

The thickness of the heat-insulating member 30 can be optionallyselected, but preferably 0.2 mm or more, more preferably 5 mm or more,still more preferably 20 mm or more. In a case where the heat-insulatingmember 30 is too thin, a sufficient heat-insulating effect may not beachieved. It is preferable that the thickness of the heat-insulatingmember 30 is half or less of a length of the single crystal finallymanufactured. The length of the single crystal indicates a length in thevertical direction of the single crystal C after crystal growth (thegrowth amount of the single crystal C). In a case where the growthamount of the single crystal is 100 mm, the thickness of theheat-insulating member 30 is preferably 50 mm or less. In a case wherethe growth amount of the single crystal is 50 mm, the thickness of theheat-insulating member 30 is preferably 25 mm or less. In a case wherethe thickness of the heat-insulating member 30 is too thick, themovement of the heat-insulating member 30 is inhibited. If the thicknessof the heat-insulating member 30 falls within the range described above,a temperature difference can be formed in the vertical direction withinthe single crystal C via the heat-insulating member 30. Consequently, itis possible to prevent the raw material gas from being recrystallized ina portion other than the surface Ca of the single crystal C.

As described above, according to the above-described SiC single crystalmanufacturing apparatus, the position of the heat-insulating member canbe controlled relatively to the crystal-grown single crystal. It ispossible to freely control the temperature distribution in the vicinityof the surface of the single crystal C during crystal growth bycontrolling the position of the heat-insulating member. Since the singlecrystal C grows along an isothermal surface, controlling the temperaturedistribution in the vicinity of the surface of the single crystal Cleads to controlling the shape of the single crystal C.

A growth method of a SiC single crystal uses the SiC single crystalmanufacturing apparatus stated above. Hereinafter, a case where the SiCsingle crystal manufacturing apparatus 100 as shown in FIG. 4 isemployed will be described as an example.

The growth method of the SiC single crystal according to the embodimentincludes a crystal growth step of growing the single crystal C from theseed crystal S installed in the seed crystal installation part 11. Thesingle crystal C is grown by recrystallization of the raw material gassublimated from the raw material G on a surface of the seed crystal S.The raw material G is sublimated by heating the crucible 10 with aheater provided outside. The sublimed raw material gas is supplied tothe seed crystal S along the guide member 20.

In the growth method of the SiC single crystal according to the presentembodiment, the positional relationship between the lower surface 30 aof the heat-insulating member 30 and the surface Ca of the singlecrystal C is controlled in a process of performing crystal growth of thesingle crystal C from the seed crystal S. The shape of the surface Ca ofthe single crystal C can be freely controlled by controlling such apositional relationship.

FIG. 7 shows the positional relationship between the lower surface 30 aof the heat-insulating member 30 and the surface Ca of the singlecrystal C, and the relationship between the positional relationship andthe isothermal surface in the vicinity of the single crystal C. FIG. 7Ais an example in a case where the surface Ca (crystal growth surface) ofthe single crystal C is flat. FIG. 7B is an example in a case where thesurface Ca (crystal growth surface) of the single crystal C is concave.FIG. 7C is an example in a case where the surface Ca (crystal growthsurface) of the single crystal C is convex.

As shown in FIGS. 7A to 7C, the shape of the surface Ca of the singlecrystal C varies depending on the position of the heat-insulating member30 with respect to the surface Ca of the single crystal C. As shown inFIG. 7A, in a case where the position of the surface Ca of the singlecrystal C and the position of the lower surface 30 a of theheat-insulating member 30 are substantially the same, the surface Ca ofthe single crystal C is flat. As shown to FIG. 7B, in a case where thelower surface 30 a of the heat-insulating member 30 is disposed closerto the raw material G side than the surface Ca of the single crystal C,the surface Ca of the single crystal C is concave. As shown in FIG. 7C,in a case where the surface Ca of the single crystal C is disposedcloser to the raw material G than the lower surface 30 a of theheat-insulating member 30, the surface Ca of the single crystal C isconvex. That is, a convex shape is formed downward. A dotted line in thedrawing indicates the isothermal surface T.

The shape of the surface Ca of the single crystal C varies depending onthe position of the heat-insulating member 30 with respect to thesurface Ca of the single crystal C because the shape of the isothermalsurface T varies in the film formation space K. FIGS. 8A and 8B arediagrams schematically showing the shape of the isothermal surface T inthe vicinity of the single crystal C during crystal growth. FIG. 8A is aview in a case where the heat-insulating member 30 is not provided. FIG.8B is a view in a case where the heat-insulating member 30 is provided.

The single crystal C of SiC has a thermal insulation effect due to itslow thermal conductivity. Meanwhile, the guide member 20 has higherthermal conductivity than that of the single crystal C. Consequently, asshown in FIG. 8A, the isothermal surface T in a case where theheat-insulating member 30 is not provided is formed so as to expand fromthe single crystal C. The crystal growth surface of the single crystal Cgrows along the isothermal surface T. Therefore, in a case where theheat-insulating member 30 is not provided, the shape of the surface Ca(crystal growth surface) of the single crystal C is fixed in a concaveshape.

On the other hand, in a case where the heat-insulating member 30 isprovided as shown in FIG. 8B, the shape of the isothermal surface Tvaries. The shape of the isothermal surface T can be freely designed bycontrolling the position of the heat-insulating member 30 with respectto the single crystal C. Controlling the position may correspond tomoving the position in at least one of a lateral direction, alongitudinal direction, and an oblique direction. Designing the shape ofthe isothermal surface T can be carried out with high accuracy byconfirming the shape in advance by simulation or the like. Thus theshape of the surface Ca of the single crystal C can be freely designedby controlling the position of the heat-insulating member 30 withrespect to the single crystal C.

In addition, controlling the position of the heat-insulating member 30with respect to the single crystal C provides the advantageous effectsof suppressing adhesion of polycrystals to the guide member 20 and ofreducing the temperature difference in an in-plane direction in thesingle crystal C.

Polycrystals are formed in a low temperature portion in the vicinity ofthe crystal growth surface of single crystal C. For example, as shown inFIG. 8A, in a case where the temperature difference between the singlecrystal C and the guide member 20 is large, polycrystals grow on theguide member 20. If the polycrystals grown on the guide member 20 comesin contact with the single crystal C, the crystallinity of the singlecrystal C is disturbed to cause defects. On the other hand, as shown inFIG. 8B, in a case where the heat-insulating member 30 is in thevicinity of the surface Ca of the single crystal C, the temperaturedifference between the single crystal C and the guide member 20 can bereduced, thereby suppressing growth of polycrystals.

Additionally, if the temperature difference in the in-plane direction inthe single crystal C is large, stress occurs in the process of growingthe single crystal C. The stress occurred in the single crystal Cproduces distortion, deviation or the like, in a crystal plane.Distortion in the single crystal C or the deviation of a lattice planemay cause killer defects such as basal plane dislocation (BPD).

The detailed description has been described that the shape of thesurface Ca (lower main surface) of the single crystal C can becontrolled. The shape of the surface Ca of the single crystal C ispreferably flat or convex toward the raw material G, because if theshape of the surface Ca of the single crystal C is concave toward theraw material G, the quality is inferior. Adjusting the shape of thesurface Ca of the single crystal C to be flat or convex, the positionsof the surface Ca of the single crystal C and the lower surface 30 a ofthe heat-insulating member 30 are substantially the same, oralternatively, the surface Ca of the single crystal C is disposed closerto the raw material G than the lower surface 30 a of the heat-insulatingmember 30.

The term “substantially the same” does not mean that the positions ofthe surface Ca of the single crystal C and the lower surface 30 a of theheat-insulating member 30 must be completely at the same height; itmeans that slight misalignment is allowed to the extent which theisothermal surface T is not greatly affected. In particular, if thelower surface 30 a of the heat-insulating member 30 is disposed within30 mm from the surface Ca of the single crystal C, the surface Ca of thesingle crystal C and the lower surface 30 a of the heat-insulatingmember 30 have the positional relationship that they are substantiallythe same. In order to adjust the shape of the surface Ca of the singlecrystal C to be flat, it is preferable that the surface Ca of the singlecrystal C and the lower surface 30 a of the heat-insulating member 30has the positional relationship that they are nearly identical. It isalso preferable that the lower surface 30 a of the heat-insulatingmember 30 is disposed within 20 mm from the surface Ca of the singlecrystal C, more preferable that the lower surface 30 a of theheat-insulating member 30 is disposed within 10 mm.

The surface Ca of the single crystal C is preferably disposed closer tothe raw material G than the lower surface 30 a of the heat-insulatingmember 30. That is, it is preferable that the lower surface 30 a of theheat-insulating member 30 is disposed closer to the seed crystalinstallation part 11 than the surface Ca of the single crystal C.Accordingly, even when an external factor such as a temperaturefluctuation in the film forming space K occurs, the concave shape of thesurface Ca of the single crystal C can be prevented.

It is preferable to control the position of the heat-insulating member30 from the start of crystal growth. That is, it is preferable tocontrol the positional relationship between the lower surface 30 a ofthe heat-insulating member 30 and the surface of the seed crystal S atthe start of crystal growth.

Immediately after the start of crystal growth, the seed crystalinstallation part 11 is provided around the seed crystal S, and adistance between the seed crystal S and the crucible 10 is also close.Therefore, the isothermal surface T in the film formation space K isalso influenced by temperature (thermal conductivity) of these members.That is, the effect exerted by using the heat-insulating member 30 isthe strongest in a region where the single crystal C has grown 30 mm ormore from the seed crystal S. However, it does not mean that theheat-insulating member 30 does not provide any advantageous effectimmediately after the start of crystal growth.

For example, in a case where the shape of the crystal growth surface ofsingle crystal C immediately after crystal growth is concave withoutproviding the heat-insulating member 30, it is necessary to return theshape of the crystal growth surface of the single crystal C to a convexshape in the subsequent growth process. If the shape of the crystalgrowth surface changes from concave to convex in the growth process,stress is accumulated in the single crystal C, and defects are likely tooccur. Therefore, the position of the heat-insulating member 30 ispreferably controlled from the start of crystal growth. The positionalrelationship of the heat-insulating member 30 to the seed crystal S canbe designed in the same manner as the positional relationship betweenthe heat-insulating member 30 and the single crystal C in the process ofcrystal growth.

<Fabrication Process of SiC Single Crystal Substrate>

The process of fabricating a SiC single crystal substrate from theobtained SiC single crystal ingot includes a flattening processinvolving lapping using a predetermined polishing slurry and a processof removing a work-affected layer. In the fabrication of a SiC singlecrystal substrate, lapping can be performed using a slurrycharacteristic of lapping. Other than that, known methods can be usedfor processing from SiC single crystal ingots to obtaining SiC singlecrystal substrates. The lapping process is described below.

Next, the available lapping slurries are detailed.

In the processing process of the free abrasive grain method, slurrycontaining, for example, water, boron carbide abrasive grains, and anadditive for dispersing the boron carbide abrasive grains is suppliedbetween the upper and lower surface plates, and pressure is applied tothe SiC substrate 1 by the upper surface plate 21 and the lower surfaceplate to flatten the surface of the SiC substrate 1. The slurry used inthe processing process is a slurry containing, for example, water as themain component. When a slurry containing water as the main component isused, the dispersibility of the boron carbide abrasive grains isenhanced and secondary aggregation is less likely to occur in theprocessing process. When a slurry containing water as a main componentis used, the surface of the SiC substrate on the upper surface plateside where the slurry feed hole is provided is cleaned by the directsupply of water, and the surface of the SiC substrate on the lowersurface plate side where the slurry feed hole is not provided is cleanedby the water supplied through the gap between the SiC substrate and thecarrier plate. The slurry used in the lapping process is collected in atank and fed again from the tank.

The modified Mohs hardness (14) of the boron carbide abrasive grain isslightly larger than the modified Mohs hardness (13) of the SiCsubstrate as an object to be polished and smaller than the modified Mohshardness (15) of the diamond. Therefore, by using such a slurry, theprocessing speed can be relatively increased while the generation ofcracks on the SiC substrate having the modified Mohs hardness (13) issuppressed, and the decrease in the grain size of the boron carbideabrasive grain can be suppressed.

The ratio of boron carbide abrasive grains in the slurry is, forexample, 15 mass % or more and 45 mass % or less, preferably 20 mass %or more and 40 mass % or less, and more preferably 25 mass % or more and35 mass % or less. When the ratio of the boron carbide abrasive grainsin the slurry is 15 mass % or more, the content of the boron carbideabrasive grains in the slurry can be increased and the processing speedof the lapping process can be enhanced. In addition, when the ratio ofthe boron carbide abrasive grains in the slurry is 45 mass % or less,the frequency and area of contact between the boron carbide abrasivegrains can be suppressed, and it is easy to suppress the decrease in thegrain size of the boron carbide abrasive grains and the abrasion of theboron carbide abrasive grains.

The boron carbide abrasive grain in the slurry used in the processingprocess has an average grain size of, for example, 15 μm or more and 40μm or less is preferably 25 μm or more and 35 μm or less. By using boroncarbide abrasive grains with an average grain size of 15 μm or more, itis easy to increase the processing speed for lapping the surface of theSiC substrate 1, and furthermore, it is possible to attach sufficientadditives to the surface, which leads to improvement in dispersibilityand suppression of decrease in grain size. In addition, by making theaverage grain size less than 40 μm, it is easy to obtain the effect ofsuppressing cracks or fissures in the SiC substrate, and furthermore, itis possible to suppress the excessive adhesion of additives describedlater to the surface and to suppress the decrease in the processingspeed due to the decrease in the contact area with the SiC substrate asa workpiece. In addition, by using such boron carbide abrasive grains,it is easy to suppress the change in particle size before and afterlapping. Here, the average grain size of the above boron carbideabrasive grain is the average grain size of the boron carbide abrasivegrain before processing, and the average grain size of the boron carbideabrasive grain after processing is, for example, 14 μm or more and 48 μmor less, and preferably 23 μm or more and 42 μm or less, because theratio of the average grain size of the boron carbide abrasive grainbefore and after processing is 0.91 to 1.2.

Here, the average grain size of the boron carbide abrasive grain ismeasured based on the particle size distribution measured by laserscattering light measurement using a particle size distributionmeasuring device Mastersizer Hydro 2000 MU (Spectris Co., Ltd.) or MT3000 Type II (Microtrack Bell Co., Ltd.).

As an additive, polyalcohols, esters and their salts, homopolymers andtheir salts, copolymers and the like can be used. Specific examplesinclude one or more substances selected from the group consisting ofglycerin, 1-vinylimidazole, sodium palm oil fatty acid methyl taurine,sodium laurate amide ether sulfate, sodium myristate amide ethersulfate, polyacrylic acid and acrylic acid-maleic acid copolymers.

These additives are thought to enhance the dispersibility of boroncarbide abrasive grains in the slurry.

The additive adheres to the surface of the boron carbide abrasive grainand inhibits direct contact between the boron carbide abrasive grains.In this way, the additive enhances the dispersibility of the boroncarbide abrasive grains in the slurry and suppresses the grain sizereduction of the abrasive grains in the processing process.

The percentage of the additive in the slurry is, for example, 3 volume %or more and 20 volume % or less, preferably 5 volume % or more and to 15volume % or less, and preferably 10 volume % or more and to 15 volume %or less. Here, the ratio of additive in the slurry refers to the ratioof the volume of additive (additive components) such as glycerin dividedby the volume of the slurry. When the additive in the slurry is withinthe above range, it adheres to the surface of the boron carbide in theslurry in a necessary and sufficient manner to obtain a favorable degreeof dispersion of the boron carbide abrasive grain in the slurry, and itis easy to suppress the decrease in the grain size of the boron carbideabrasive grain in the processing process.

In this lapping process, the processing speed for processing the surfaceof the SiC substrate in the processing process is, for example, 14 μm/hor more and 45 μm/h or less, preferably from 16 km/h or more and 40 μm/hor less, and more preferably from 18 μm/h or more and 25 μm/h or less.The processing speed depends on the processing pressure described aboveand the average grain size of the boron carbide abrasive grains. It iseasy to obtain the effect of suppressing the decrease in the grain sizeof the boron carbide abrasive grain and the abrasion of the boroncarbide abrasive grain by setting the processing speed to 45 μm/h orless. The throughput can be increased by increasing the processing speedto 14 μm/h or more. When lapping processing is performed in multiplebatches, the processing speed obtained by dividing the total change inthe thickness of the SiC substrate by the total processing time may bewithin the above range, and it is preferable that the processing speedat any timing is within the above range. That is, when lapping isperformed in multiple batches, it is preferable that the processingspeed calculated in each batch is within the above range.

Here, the processing speed is calculated from the difference in thethickness of the SiC substrate 1 before and after lapping and theprocessing time. Specifically, the processing speed is calculated by thefollowing method. The measurement positions of the thickness of the SiCsubstrate 1 are position 1 e corresponding to the center of the SiCsubstrate before the formation of the orientation flat OF on the SiCsubstrate 1, position 1 a being 5 mm to 10 mm away from the midpoint ofthe orientation flat OF toward the position 1 c, position 1 b on thesame straight line c as positions 1 a and 1 c and being 5 mm to 10 mmaway in the direction of position 1 a from the outer periphery of theSiC substrate 1, and positions 1 d and 1 e on the straight lineperpendicular to the straight line c and being 5 mm to 10 mm away in thedirection of position 1 a from the outer periphery of the SiC substrate1. The thickness of SiC substrate 1 at these five positions 1 a to 1 eis measured by an indicator (ID-C 150 XB, made by Mitsutoyo), and theobtained thickness is treated as the thickness of SiC substrate 1. Theprocessing speed is calculated by dividing the difference in thethickness (micrometers) of the SiC substrate 1 before and after theprocessing thus obtained by the processing time (h).

Adhesion of additives to the surface of the boron carbide abrasivegrains in the slurry used in the processing process increases thedispersibility of the boron carbide abrasive grains, and the contact ofthe boron carbide abrasive grains can be suppressed, so that thedecrease in the grain size of the boron carbide abrasive grains can besuppressed.

Specifically, the change in the grain size of the boron carbide abrasivegrain can be suppressed to the extent that the ratio of the averagegrain size of the boron carbide abrasive grain after processing to theaverage grain size of the boron carbide abrasive grain before processingis 0.91 to 1.2 in the processing process. The reason why the ratioincludes a value greater than 1 is that, in the processing process,boron carbide abrasive grains are secondarily agglomerated, and thegrain size of some boron carbide abrasive grains may be larger than thatbefore processing.

In the conventional lapping process, since the grain size of the boroncarbide abrasive grain in the slurry is greatly reduced by lappingprocess, it is necessary to add abrasive grain to the slurry each timethe lapping process is performed again, and each time it is necessary tocarry out complicated management to obtain the distribution of the grainsize of the abrasive grain in the slurry depending on the number ofbatches used for lapping process.

In this way, this lapping process facilitates the management of thegrain size of the boron carbide abrasive grain and reduces the cost, inaddition to reducing the environmental load and suppressing theoccurrence of cracks.

In addition, since the grain size of the boron carbide abrasive grainsdoes not change much in this lapping process, the change in theprocessing speed during lapping process can be restrained and thelapping process can be continued under the same conditions. This lappingprocess is particularly effective when using boron carbide, which has aslightly higher modified Mohs hardness than silicon carbide as an objectto be polished. Because such abrasive grains and substrates are used inthis lapping process, it is also possible to suppress cracks that occurfrequently when diamond is used as abrasive grains and SiC substratesare used as objects to be polished.

In addition, since this lapping process can suppress the decrease in thegrain size and abrasion of the boron carbide abrasive grain, thedispersion of the grain size of the boron carbide abrasive grain in theslurry during lapping process is reduced. While the processing speed ofthe lapping process depends on the grain size of the abrasive grainused, in this lapping process, since the variation in the grain size ofthe abrasive grain can be suppressed, the whole surface of the SiCsubstrate is processed by the abrasive grain of approximately equalgrain size, and the in-plane variation of the substrate thickness of theSiC substrate after processing is reduced.

EXAMPLES

Examples of the disclosure are described below, but the disclosure isnot limited to the following examples.

Example 1

First, a SiC single-crystal ingot was fabricated using the SiC singlecrystal manufacturing apparatus shown in FIG. 4 .

A 4H-SiC single crystal having a surface with an off angle of 4° withrespect to the (0001) plane, as a main surface, a diameter of 200 mm anda thickness of 5.0 mm was used as the seed crystal S. In the early stageof crystal growth, the crucible temperature was controlled so that thetemperature (Tr) in the vicinity of the same height as the seed crystalsurface on the side wall of the crucible body was 30° C. to 150° C., thetemperature (Tg) in the center of the seed crystal in the plan view ofthe outer wall of the crucible lid was 50° C. to 250° C., and thetemperature difference (ET) between Tr and Tg was 20° C. to 100° C. Inaccordance with the crystal growth, the crystal growth was carried outwhile gradually moving the heat-insulating member 30 so that the endface (lower surface 30 a in FIG. 7C) of the raw material side of theheat-insulating member 30 was closer to the lid than the growth surfaceof the single crystal and the distance in the growth direction betweenthe end face of the raw material side of the heat-insulating member 30and the growth surface of the single crystal was within 10 mm.

The SiC single crystal ingot thus obtained was 208 mm in diameter and20.2 mm in height.

Then, a SiC single crystal substrate having an off angle of 4° withrespect to the (0001) plane and a thickness of 0.9 mm was obtained by aknown processing method.

For this SiC substrate, the thickness of the SiC substrate was measuredat five positions as shown in FIG. 1 , and the average was taken as thethickness of the SiC substrate.

Then, the SiC single crystal substrate whose thickness was measured wasplaced on the carrier plate of the polishing device and lapped. Thelapping slurry was obtained by adding a predetermined amount of boroncarbide abrasive grains and AD8 (10 vol %) as an additive to water anddispersing. The grain size F 320 (JIS R 6001) was used as the boroncarbide abrasive grain. Here, the proportion of glycerin (made byAichemitechno Co., Ltd.) as an additive in the slurry was set at 6 vol%.

The lapping process was performed by the free abrasive grain methodwhile the lapping slurry was supplied at a rate of 16 L/min. The lappingslurry was cycled and used.

The driving conditions of the polishing device in the lapping processwere as follows: processing pressure 160 g/cm², lower surface speed 16rpm, upper surface speed 5.5 rpm, center gear speed 2.8 rpm, internalgear speed 6.0 rpm, and processing time 40 minutes.

After lapping, the particle size distribution of the boron carbideabrasive grains in the slurry was measured in the same manner as beforelapping, and the thickness of the substrate was measured in the samemanner as before lapping, and the processing speed was calculated. Inthis lapping process, the average processing speed of 15 SiC substrateswas 18 μm/h.

After the measurements were made, the slurry used in the previouslapping process was fed and a second lapping process and measurementswere performed while circulating the slurry. In Example 1, this wasrepeated and a total of eight lapping and measurements were performed.

Then, an etching process for removing the work-affected layer and a CMPprocess for mirror-polishing were performed to obtain the SiC singlecrystal substrate of Example 1.

Example 2

A SiC single crystal substrate was obtained under the same conditions asin Example 1 in the preparation of the SiC single crystal ingot, exceptthat the temperature at the highest temperature point of the rawmaterial was raised by 20° C., the driving conditions of the polishingapparatus in the lapping process were adjusted so that the in-planevariation in substrate thickness after lapping was smaller than inExample 1.

Comparative Example 1

A SiC single crystal substrate was obtained under the same conditions asin Example 1, except that using a SiC single crystal manufacturingapparatus without a heat-insulating material 30, using a seed crystal Swith a diameter of 150 mm, Tr, Tg, and AT were not controlled during thecrystal growth, and lapping slurry containing no additive (AD8) was usedin the lapping process.

Comparative Example 2

A SiC single crystal substrate was obtained under the same conditions asin Comparative Example 1 except that the temperature of the highesttemperature point of the raw material was changed to increase by 10° C.

Comparative Example 3

A SiC single crystal ingot was prepared using a SiC single crystalmanufacturing apparatus without heat-insulating member 30, and a SiCsingle crystal substrate was obtained under the same conditions as inExample 1 except that lapping slurry containing no additive (AD8) wasused in the lapping process.

Comparative Example 4

The SiC single crystal substrate was obtained under the same conditionsas in Comparative Example 3 except that the thickness of the seedcrystal was changed to 4.0 mm and the temperature of the highesttemperature point of the raw material was increased by 80° C.

Comparative Example 5

The SiC single crystal substrate was obtained under the same conditionsas in Comparative Example 3 except that the thickness of the seedcrystal was changed to 3.5 mm and the temperature of the highesttemperature point of the raw material was increased by 70° C.

(Evaluation)

For the SiC single crystal substrates of Example 1, Example 2, andComparative Example 1 to Comparative Example 5, SORI, in-plane variationin the thickness of the substrate, number of micropipes, total number ofdislocations, the density of threading dislocation (TD) and the densityof basal plane dislocation were evaluated. The number of micropipes, thetotal number of dislocations, the density of threading dislocation (TD)and the density of basal plane dislocation were evaluated based on etchpits appearing by KOH etching performed at 550° C. for 10 minutes. Theresults are shown in Table 1. The density of TD etch pits in Table 1 arethe sum of the density of TSD etch pits and the density of TED etchpits.

TABLE 1 Use of heat- in-plane thickness insulating Total number Densityof TD Density of BPD SORI distribution after in-plane thickness memberof etch pits etch pits [/cm²] etch pits [/cm²] [μm] lapping [μm]distribution [μm] Example 1 ◯ 1.2 × 10⁶ 400 310 21 1.2 1.3 Example 2 ◯2.1 × 10⁶ 450 500 14 0.9 0.9 Comparative Example 1 X 5.6 × 10⁶ 1500 240030 2.2 2.4 Comparative Example 2 X 6.6 × 10⁶ 2300 3600 28 2.6 2.5Comparative Example 3 X 5.1 × 10⁷ 1900 4300 45 2.8 2.9 ComparativeExample 4 X 5.0 × 10⁹ 4200 4100 60 2.5 2.6 Comparative Example 5 X 5.2 ×10⁹ 5950 7300 67 2.3 2.4

The densities of micropipe defects in Example 1, Example 2, andComparative Example 1 to Comparative Example 5 was 1/cm² or less.

Both SORI and the in-plane variation in the thickness of the substratewere greatly reduced in Example 1 and Example 2 compared to ComparativeExample 1 to Comparative Example 5.

The total number of the etch pits was significantly reduced in Example 1and Example 2 (8-inch substrates) compared to Comparative Example 1 andComparative Example 2 (6-inch substrates), and both the density of TDetch pits and the density of BPD etch pits were greatly reduced inExample 1 and Example 2(8-inch substrates) compared to ComparativeExample 1 and Comparative Example 2 (6-inch substrates). The results areconsidered to be the result of more precise temperature control inExample 1 and Example 2.

The total number of the etch pits, the density of TD etch pits and thedensity of BPD etch pits were greatly reduced in Example 1 and Example 2(8-inch substrates) compared to Comparative Example 3 to ComparativeExample 5 (8-inch substrates). From the results, it was found that theinfluence of more precise temperature control is greater in theproduction of 8-inch SiC single crystal substrates than in theproduction of 6-inch SiC single crystal substrates.

EXPLANATION OF REFERENCES

-   -   1 SiC single crystal substrate

What is claimed is:
 1. An 8-inch SiC single crystal substrate, wherein the diameter is in a range of 195 mm to 205 mm, the thickness is in a range of 300 μm to 650 μm, SORI is 50 μm or less, and the in-plane variation of the thickness of the substrate, which is the difference between the maximum and minimum substrate thickness at the center of the substrate and four points on the circumference of a circle having a radius half the radius of the substrate, is 1.5 μm or less.
 2. The 8-inch SiC single crystal substrate according to claim 1, wherein the SORI is 40 μm or less.
 3. The 8-inch SiC single crystal substrate according to claim 1, wherein the SORI is 30 μm or less.
 4. The 8-inch SiC single crystal substrate according to claim 1, wherein the SORI is 20 μm or less.
 5. The 8-inch SiC single crystal substrate according to claim 1, wherein the in-plane variation of the thickness of the substrate is 1.0 μm or less.
 6. The 8-inch SiC single crystal substrate according to claim 2, wherein the in-plane variation of the thickness of the substrate is 1.0 μm or less.
 7. The 8-inch SiC single crystal substrate according to claim 3, wherein the in-plane variation of the thickness of the substrate is 1.0 μm or less.
 8. The 8-inch SiC single crystal substrate according to claim 4, wherein the in-plane variation of the thickness of the substrate is 1.0 μm or less.
 9. The 8-inch SiC single crystal substrate according to claim 1, wherein the density of micropipe defects is 1/cm² or less, and the total number of etch pits appearing by KOH etching performed at 550° C. for 10 minutes is 5×10⁹ or less.
 10. The 8-inch SiC single crystal substrate according to claim 9, wherein the total number of etch pits is 5×10⁸ or less.
 11. The 8-inch SiC single crystal substrate according to claim 10, wherein the total number of etch pits is 5×10⁷ or less.
 12. The 8-inch SiC single crystal substrate according to claim 9, wherein the density of etch pits identified as threading dislocations is 2×10³/cm² or less, and the density of etch pits identified as basal plane dislocations is 5×10³/cm² or less.
 13. The 8-inch SiC single crystal substrate according to claim 10, wherein the density of etch pits identified as threading dislocations is 2×10³/cm² or less, and the density of etch pits identified as basal plane dislocations is 5×10³/cm² or less.
 14. The 8-inch SiC single crystal substrate according to claim 11, wherein the density of etch pits identified as threading dislocations is 2×10³/cm² or less, and the density of etch pits identified as basal plane dislocations is 5×10³/cm² or less. 